The present invention relates to a remediation process for the insulation of power cables and, more particularly, to injection of dielectric enhancement component into the power cable.
A remediation process for the insulation of high-voltage electrical power cables requires the injection of a remediation fluid into the cables. It is known in the art that remediation fluids which are most effective have viscosities less than 50 centistokes at 25xc2x0 C. as these fluids must be able to flow through very small interstitial spaces over very long cable lengths and must be of small enough molecular size to diffuse into the cable insulation. In many instances, this injection process takes place while the cable is energized. When the remediation process is performed on energized cables, a class of special cable end terminations is typically used. These terminations are known as injection elbows. Injection elbows are similar to industry standard elbow-type connectors except that special ports have been designed into them to allow for the attachment of an injection plug to the elbows.
After injection of the remediation fluid is complete, the injection plug is withdrawn from the injection port and is replaced with a sealing plug. Between the time that the injection plug is removed, and the sealing plug is installed, the injection port is open, and the energized conductor of the cable is exposed. Because of the remediation fluid""s low viscosity it is likely to empty out of the open injection port. Although there is no direct electrical connection between the conductor and the grounded exterior of the cable elbow, there is the danger of an indirect electrical connection being established between the conductor and the grounded exterior of the elbow.
One such indirect pathway may be formed by contaminants that have become entrained in the remediation fluid. Contaminated fluid can be drawn from the injection port as the injection plug is withdrawn or may simply flow out under the force of gravity, thereby creating partial discharging or even a complete conductive pathway to the ground plane.
A second indirect pathway is created by source molecules such as those found in low viscosity remediation fluid, water or other contaminants which may be present in the conductor. Source molecules, also referred to as particles, can ionize or form an aerosol, which may become charged in the high-voltage field. These ionized or charged particles may then accelerate towards the ground plane creating a dynamic and conductive aerial pathway.
These two known conductive pathways, as well as any other conductive pathway established between the conductor and the ground plane, can degrade or destroy the injection elbow. Therefore, a need exists to create a barrier to block the conductive pathway between the conductive portion of the cable and the ground plane to increase the life expectancy of the injection elbow.
One embodiment of the present invention is directed towards a method and apparatus for creating a barrier after the injection of remediation fluid to block the conductive pathway between the conductive portion of an energized cable and the ground plane. An injection elbow with an injection port is used to introduce remediation fluid into the energized cables. The remediation fluid is introduced into the injection port by way of an injection plug inserted into the injection port. Upon completion of the introduction of the remediation fluid, an insulation material is injected through an injection tube of the injection plug and into the injection port. This insulation material may be any of a variety of dielectric, high-viscosity fluids. The insulation material effectively blocks the conductive pathway between the conductive portion of the cable and the ground plane so as to allow removal of the injection plug without creation of a conductive pathway to allow for the insertion of a permanent plug to block the injection port and protect the injection elbow from degradation.
In another embodiment of the present invention, the injection elbow includes a flap valve located between the injection port and a fluid chamber inside the injection elbow. As fluid is introduced through the injection port, the flap valve is opened either by the fluid pressure, or by an extension on the injection plug, allowing the fluid to fill a chamber in the injection elbow. When the chamber in the fluid elbow is full and introduction of the fluid has ceased, the pressure from inside the chamber forces the flap valve to shut, thus creating a barrier between the conductor and the ground plate. The injection plug can now be removed without exposing the energized conductor which may create a degradation of the injection elbow.
In still another embodiment of the present invention, a physical barrier is incorporated in the injection plug to block the escape of remediation fluid upon discontinuing filling of the chamber of the injection elbow. This embodiment permits leaving behind the injection plug in the injection port thus eliminating a need for a permanent plug. The physical barrier of this embodiment includes a ball valve; however, a variety of gate valves or check valves, actuated manually, electronically, hydraulically, or pneumatically may be used.
In yet another embodiment of the present invention, the injection plug includes a breakable tip having a catch at its end. Upon insertion of the injection tube into the injection port, the breakable tip becomes lodged in the injection port. After discontinuing the introduction of remediation fluid into the chamber, the injection plug is removed causing the breakable tip of the injection tube to remain lodged in the injection port creating a permanent barrier in the injection port, therefore, blocking the conductive pathway between the conductive portion of the cable and the ground plane.